__________Applications Information
Power-Supply Considerations
Overview
The MAX4530/MAX4531/MAX4532 construction is typi-
cal of most CMOS analog switches. They have three
supply pins: V+, V-, and GND. V+ and V- drive the
internal CMOS switches and set the limits of the analog
voltage on any switch. Reverse ESD-protection diodes
are internally connected between each analog-signal
pin and both V+ and V-. One of these diodes conducts
if any analog signal exceeds V+ or V-. During normal
operation, these and other reverse-biased ESD diodes
leak, forming the only current drawn from V+ or V-.
Virtually all of the analog leakage current comes from
the ESD diodes. Although the ESD diodes on a given
signal pin are identical and therefore fairly well bal-
anced, they are reverse-biased differently. Each is
biased by either V+ or V- and the analog signal. This
means their leakages vary as the signal varies. The
difference in the two diode leakages to the V+ and V-
pins constitutes the analog-signal-path leakage current.
All analog leakage current flows between each pin and
one of the supply terminals, not to the other switch ter-
minal. For this reason, both sides of a given switch can
show leakage currents of either the same or opposite
polarity.
The analog-signal paths and GND are not connected.
V+ and GND power the internal logic and logic-level
translators, and set both the input and output logic lim-
its. The logic-level translators convert the logic levels
into switched V+ and V- signals to drive the analog sig-
nals’ gates. This drive signal is the only connection
between the logic supplies and signals and the analog
supplies. V+ and V- have ESD-protection diodes to
GND.
The logic-level thresholds are TTL/CMOS compatible
when V+ = +5V. As V+ rises, the threshold increases
slightly, so when V+ reaches +12V, the threshold is
about 3.1V—above the TTL guaranteed, high-level min-
imum of 2.8V, but still compatible with CMOS outputs.
Bipolar Supplies
The MAX4530/MAX4531/MAX4532 operate with bipolar
supplies between ±2.0V and ±6V. The V+ and V- sup-
plies need not be symmetrical, but their sum cannot
exceed the +13V absolute maximum rating.
Single Supply
The MAX4530/MAX4531/MAX4532 operate from a sin-
gle supply between +2V and +12V when V- is connect-
ed to GND. All of the bipolar precautions must be
observed. At room temperature, they actually work with
a single supply at, near, or below +1.7V, although as
supply voltage decreases, switch on-resistance and
switching times become very high.
High-Frequency Performance
In 50Ω systems, signal response is reasonably flat up
to 50MHz (see Typical Operating Characteristics).
Above 20MHz, the on response has several minor
peaks that are highly layout-dependent. The problem is
not in turning the switch on, but in turning it off. The off-
state switch acts like a capacitor and passes higher
frequencies with less attenuation. At 10MHz, off isola-
tion is about -65dB in 50Ω systems, becoming worse
(approximately 20dB per decade) as frequency
increases. Higher circuit impedances also make off iso-
lation worse. Adjacent channel attenuation is about 3dB
above that of a bare IC socket, and is due entirely to
capacitive coupling.
MAX4530/MAX4531/MAX4532
Low-Voltage, CMOS Analog Multiplexers/Switches
with Enable Inputs and Address Latching
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